1. Field of the Invention
The present invention relates to a boundary line detecting method for specifying, by image processing, a boundary line between areas different in reflected light intensity, as well as a positioning method and apparatus for positioning, using the detecting method, for example a magnetic head body for a hard disk device and a support member such as a load beam relative to each other.
2. Description of the Prior Art
FIG. 8A is a plan view showing a conventional magnetic head positioning apparatus and FIG. 8B is a side view thereof.
A magnetic head body 1, which is for a hard disk device, comprises a slider and a recording portion and a reproducing portion both of a thin film structure disposed at a trailing-side end portion of the slider. A load beam 2 as a support member for supporting the head body 1 is formed using a plate spring material. At a tip portion of the load beam 2 the head body 1 is supported through a thin plate spring called flexure. A pivot 3 is formed in the shape of a concave sphere at the tip of the load beam 2 and its apex is in spot contact with the upper surface of the head body. The head body 1 is supported pivotably in both rolling and pitching directions with the apex of the pivot 3 as fulcrum.
In the conventional positioning process for the head body 1 and the load beam 2, two side faces of the slider of the head body 1 are positioned and held while being pressed against stepped portions 4a and 4b which are formed perpendicularly to each other on the upper surface of a carrier 4, the carrier 4 being moved in the direction of arrow L at each step of the positioning process. The carrier 4 with the head body 1 held thereon is located at a predetermined step position between carrier positioning blocks 5, 5, at which position the load beam 2 is installed on the carrier 4.
A pair of positioning pins 4c and 4d are implanted in the upper surface of the carrier 4, and positioning holes 2a and 2b formed in the load beam 2 are fitted on the positioning pins 4c and 4d, whereby the load beam 2 is positioned on the carrier 4. The load beam 2 is held with a jig in the thus positioned state on the carrier 4. In this state the flexure provided at the tip of the load beam 2 and the head body 1 are bonded and fixed together.
In the magnetic head of this type, the relative position between the head body 1 and the pivot 3 exerts a great influence on a floating posture of the head body on a recording medium such as a hard disk. However, the positioning method using the positioning apparatus shown in FIG. 8 has encountered a limit in determining a relative position between the head body 1 and the pivot 3 with a high accuracy.
More particularly, the position where the load beam 2 is to be installed is determined on the basis of the positioning holes 2a and 2b. But a machining tolerance in the relative position between the positioning holes 2a, 2b and the pivot 3 gives rise to an error in the position of the pivot 3 on the carrier 4. The head body 1 is positioned on the basis of the stepped portions 4a and 4b on the carrier 4 and therefore, as to the relative position of the pivot 3 and the head body 1, not only the aforesaid machining tolerance but also positional dimension tolerances between the stepped portions 4a, 4b and the positioning pins 4c, 4d of the carrier 4, as well as fitting clearance tolerances between the positioning pins 4c, 4d and the positioning holes 2a, 2b, are accumulated.
As a result, a maximum of about xc2x120 xcexcm tolerance occurs between a designed abutment position of the pivot 3 on the head body 1 and an actual position where the pivot 3 abuts the head body 1. When the head body 1 assumes a floating posture on a recording medium such as a hard disk, the above xc2x120 xcexcm error of the pivot position causes a difference of about xc2x17.8 nm in terms of a floating distance in the rolling direction and a difference of about xc2x11.6 nm in terms of a floating distance in the pitching direction.
Further, when the assembly of the head body 1 and the load beam 2 is incorporated in a hard disk device for example, a tolerance of about xc2x17.6 nm occurs in the floating distance of the head body 1 due to variations in static posture of the head body 1 on the recording medium or in the spring pressure of the load beam.
If the variation in the floating distance caused by the positioning error between the head body 1 and the load beam and the variation in the floating distance caused by variations in static posture or spring pressure are merely added together, the result obtained becomes very large, thus causing defective products whose variations in the floating distance of head body 1 exceed an allowable value. Consequently, the percentage defect becomes high.
Recently, with an increase in recording density, the slider of the head body 1 has become smaller in size and the floating distance of the head body has become shorter, resulting in the tolerance thereof becoming narrower. Therefore, it is necessary that the control of the floating distance be done with a high accuracy.
When attention is paid to variation factors in the floating distance, the attempt to minimize the variation in the floating distance caused by variations in static posture or spring pressure is restricted by the entire structure of the head, so in order to realize such attempt it is necessary that the relative position between the head body 1 and the pivot 3 formed in the load beam 2 be determined with a high accuracy.
As a method for determining a relative position between the head body 1 and the pivot 3, reference is here made to a method in which the bonded portion of the load beam 2 and the head body 1 and the vicinity thereof are photographed on a larger scale with a camera, then the distance between an edge portion of the slider of the head body and a central position of the pivot is determined on the image thus obtained, and a check is made to see if the distance is within the tolerance or not.
However, with such an image photographed by a camera, it is impossible to observe distances shorter than the arrangement pitch of photodetectors such as CCDs. For example, even if an attempt is made to specify an edge portion of the slider of the head body 1, it is impossible to specify its position at a distance shorter than the arrangement pitch of the photodetectors.
The present invention solves the above-mentioned problems of the prior art and it is an object of the invention to make it possible to determine a relative position between a head body and a support member.
It is another object of the present invention to make the detection of a boundary portion of, for example, a head portion possible up to a still shorter distance than the arrangement pitch of photodetectors in a camera.
According to the present invention, in one aspect thereof, there is provided a method for detecting a boundary line between areas different in light reflectance, using a camera with a large number of photodetectors arranged therein. The method comprises the steps of, subjecting an image obtained by the camera to image processing on the basis of light intensities detected by the photodetectors, when assuming that blocks where luminances corresponding respectively to the photodetectors appear on the image are unit blocks, comparing the luminances of plural unit blocks arranged in a predetermined direction, and specifying an actual position of the boundary line located in one unit block.
Preferably, variations in luminance between unit blocks arranged in the predetermined direction are derivated and the derivated value of luminance in the unit block of highest luminance and the derivated values of luminance in plural unit blocks adjacent thereto are compared to specify an actual position of the boundary line located in one unit block.
In the present invention, the use of derivation does not constitute any special limitation. Even without using derivation, an actual position of the boundary line can be predicted and specified by comparing variations in luminance between adjacent unit blocks. However, if derivation is used, variations in luminance between unit blocks, as well as noises, can be offset, and the boundary line can be specified by predicting a peak position of luminance, thus making it possible to specify the boundary line with a high accuracy.
According to the present invention, the boundary line can be specified at a still shorter distance than the arrangement pitch of unit blocks which are constant in luminance, namely, the arrangement pitch of photodetectors in a CCD camera.
In the case where the boundary line is rectilinear, it is possible to add, or take a mean value of, derivated values of luminances of unit blocks in a row of the unit blocks arranged in parallel to the extending direction of the boundary line. It is also possible to perform such addition or calculation of a mean value in plural rows of unit blocks, then compare the added values or mean values between the rows to predict a peak position of the added values or mean values in a direction intersecting the boundary line, and specify the position of the boundary line on the basis of the peak position.
Given that a derivated value of luminance in each of adjacent unit blocks in an area including the boundary line is ai (i is a positive integer) and position coordinates of each unit block are Xi (or Yi), it is possible to specify an X coordinate position (or Y coordinate position) of the boundary line in accordance with xcexa3(aixc3x97Xi)/xcexa3ai [or xcexa3(aixc3x97Yi)/xcexa3ai].
Where the boundary line is arcuate or curved, if a derivated value of luminance in each of adjacent unit blocks in an area including the boundary line is assumed to be ai (i is a positive integer) and the position of each unit block on X coordinates is Xi and that of each unit block on Y coordinates is Yi. It is possible to specify a peak position of the derivated luminance value in one unit block, and by connecting such peak positions between unit blocks it is possible to predict the boundary line.
Thus, where the boundary line is arcuate, it is possible to specify the circular arc by connecting the arc passing points in unit blocks and predict a central position of a circle on the basis of the circular arc.
According to the present invention, in another aspect thereof, there is provided a method for positioning a head body opposed to a recording medium and a support member for supporting the head body relative to each other. The method comprises the steps of: directing light to a combined portion of the head body and the support member and detecting the reflected light by means of a camera with a multitude of photodetectors arranged therein; detecting an edge portion of the head body in accordance with the boundary line detecting method described in any one of the first to fourth aspects of the invention; detecting the center of a concave pivot formed in the support member and serving as a fulcrum for pivotal motion of the head body in accordance with the boundary line detecting method described in the sixth aspect of the invention; adjusting the relative position between the head body and the support member so that the distance between the edge portion of the head body and the center of the pivot both detected in the preceding steps falls under a tolerance; and fixing the head body and the support member to each other, after the adjustment.
According to the present invention, in a further aspect thereof, there is provided a method for positioning between a head body opposed to a recording medium and a support member for supporting the head body. The apparatus comprises: a light radiating means for directing light to a combined portion of the head body and the support member; a camera with a large number of photodetectors arranged therein to detect the light reflected from the head body and the support member; an image processing means for processing an image detected by the photodetectors in the camera; and an adjusting means for adjusting the relative position between the head body and the support member so that distance between an edge portion of the head body and the center of a concave pivot both specified by the image processing means fall under a tolerance. In the image processing means, when blocks where luminances corresponding respectively to the photodetectors appear on the image are assumed to be unit blocks, luminances of plural unit blocks arranged in a predetermined direction are compared to specify an edge portion of the head body positioned in one unit block and a central position of the pivot.
In the above magnetic head positioning method and apparatus, the relative position may be adjusted by fixing the head body 1 and moving the support member, or by fixing the support member and moving the head body.
Irrespective of the above magnetic head positioning method and apparatus, the bounding line detecting method according to the present invention is applicable to the detection of the distance between other components as a method of detecting a boundary line between areas different in light reflectance.